The present invention relates to a control system for an automatic clutch such as an electromagnetic clutch for an automatic transmission of a motor vehicle.
An automobile provided with a continuously variable belt-drive transmission with an electromagnetic clutch is disclosed by the applicant of the present patent application. The electromagnetic clutch of the transmission is controlled by a control system to provide various operational modes such as a starting mode of a vehicle, reverse excitation mode, drag mode at release of an accelerator pedal of a vehicle, and mode of lock-up engagement. One of the modes is selected in accordance with a position of a selector lever and driving conditions to control the electromagnetic clutch.
Japanese Patent Application Laid-Open 60-256632 discloses a control system for an electromagnetic clutch wherein the clutch torque is generated to engage the clutch when vehicle speed is higher than a predetermined clutch engaging reference speed, even if the accelerator pedal is released, thereby producing an engine braking effect.
However, when a select lever is shifted to a reverse position during forward driving or to the drive position during rearward driving, which is hereinafter called loading shift, the clutch torque is generated to engage the clutch if the vehicle speed is higher than the predetermined speed. As a result, an extremely large torque is exerted on the transmission in the opposite direction, so that the engine is subjected to a large load, which may cause stallings of the engine.